What's the reasoning behind buying the most recent expansion card packs and getting all legendary cards first?
Based on my perspective, I thought it would be best to buy the classic card packs as the expansion card packs would be rotated out while the classic card packs would maintain in rotation therefore the best packs to buy would be the classic packs. Don't get me wrong, I'm not trying to start an argument here, just wanted to know why getting the legendary from each expansion would be the best option.
The game no longer has Classic Packs - instead, a Core Set will be given out for free each year for all players. The only packs you can buy for Standard are the expansion packs as well as generic Standard packs which include cards from all current expansions in Standard. As others have pointed out, you are best off purchasing individual packs from each expansion until you open a pack with a Legendary since you are guaranteed a Legendary within the first ten packs you open from each set. Legendary cards are pretty expensive to craft, so getting all your guaranteed Legendaries as soon as possible is the best way to give your collection a bit of a boost - you'll likely end up playing one or two decks based on the Legendaries you open.
TrumpSC is a HS streamer who regularly posts YT content for new players. He's currently doing a F2P run for Stormwind. Here's a link to the most recent episode -